Neuromyelitis optica (NMO) is a neurological disorder also known as Devic's syndrome in Western countries and as opticospinal multiple sclerosis in Asia. NMO is regarded as a severe variant of multiple sclerosis (MS), and accounts for 30% of MS cases occurring in Asians. In North America, non-Caucasians represent a higher frequency of patients with NMO than the frequency of those with classical MS. The characteristic inflammatory demyelinating lesions of NMO selectively and repeatedly affect the optic nerves and the spinal cord, thereby causing both blindness and paralysis.